The present invention relates to mixtures of 4-methyl-4-mercapto-2-pentanone or 2-methoxy-3-isobutyl pyrazine or combinations thereof in further admixture with other organic sulfur compounds suitable for the odorization of combustible hydrocarbon gases such as natural gas, vapors and gases recoverable in the refining of petroleum and other gases suitable as fuels for heating, illuminating and cooking purposes.
A number of organic sulfur compounds are known in the prior art to be effective malodorants for combustible gases. These include monomercaptans and acyclic and cyclic sulfides. Specific examples of these compounds in which percentages are by weight are the following: (1) Thiophane herein referred to as "Odorant A". (2) Refinery by-product mercaptans herein after referred to as "Odorant B". These materials are characterized by a boiling point range of about 100.degree.-215.degree. F. and comprise C.sub.2 -C.sub.4 mercaptans. Traces of C.sub.5 mercaptans are sometimes present. Typically, this odorant contains 25% ethyl mercaptan, 35% isopropyl mercaptan, 15% n-propyl mercaptan, 20% 2-butyl mercaptan, 3% isobutyl mercaptan and 2% n-butyl mercaptan, although they can be present respectively within ranges of about 1-30; 15-50; 5-25; 10-30; 1-6 and 1-4. (3) Mixed aliphatic sulfides of low molecular weight. One alkyl group may be ethyl and the other group ethyl, propyl or butyl. These compounds often contain a small amount (approximately 5%) of refinery by-product mercaptans, Odorant B, hereinafter referred to as "Odorant C". An amount as high as 10% by-product mercaptans can be present. A further specific example of mixed sulfides is a mixture of diethyl sulfide and ethyl propyl sulfide as disclosed in U.S. Pat. No. 2,823,104, the disclosure of which is incorporated by reference herein. (4) t-Butyl mercaptan. This material as an article of commerce often contains refinery by-product mercaptans (Odorant B), in an amount of 15-50% based on the two materials. A mixture of the two materials hereinafter referred to as "Odorant D" in which the refinery mercaptans are present in an amount of about 20%, the mixture having a boiling point range of about 132.degree.-185.degree. F. is a preferred example in commerce. (5) A mixture of dimethyl sulfide and refinery by-product mercaptans (Odorant B) in proportions, for example, of 90% dimethyl sulfide and 10% mercaptans hereinafter referred to as "Odorant E". As little as 5% to as high as 60% mercaptans may be present. (6) A mixture of 1,2-ethane dimercaptan together with at least one of Odorants A, B, C, D or E, hereinafter referred to as "Odorant F" as more particularly described in U.S. Pat. No. 3,404,971 issued on Oct. 8, 1968, the disclosure of which is incorporated by reference herein. Preferably about 5-20% of the ethane dimercaptan is incorporated into the mixture and the resulting mixture is used in a dosage of about 0.3 pounds per million cubic feet (m.c.f.) of hydrocarbon gas. This is indicated to have the same odor intensity as thiophane alone used at a dosage level of 1 pound per m.c.f. of the same hydrocarbon gas.
In addition, U.S. Pat. No. 3,545,949 issued on Dec. 8, 1970 discloses the use of cyclohexyl mercaptan as a gas odorant.
Japan Kokai 73/79804 discloses as an odorizing agent for gases a mixture of valeric acid and ethyl acrylate. It is also indicated in Kokai 73/79804 that this mixture may also contain triethyl amine. Kokai 73/79804 is abstracted in Chem. Abstracts 1974, Number 72614c.
A mixture of ethyl acrylate and t-butyl mercaptan is disclosed to be useful in Japan Kokai 73/79805 abstracted in Chem. Abstracts 1973, number 72615d.
Chem. Abstracts Volume 91, 1979, 60005u (abstract of U.S.S.R. Pat. No. 654668, of Mar. 30, 1979) discloses an odorant of decreased solubility in water and decreased toxicity containing ethyl mercaptan, n-propyl mercaptan, s-butyl mercaptan, isobutyl mercaptan, and n-butyl mercaptan.
German Offenlegungsschrift 2337782 of Feb. 13, 1975 abstracted in Chem. Abstracts 1975, number 45671z, discloses odorization of liquified natural gas by the addition of about 10 volume percent of ethane thiol or methane thiol solutions in propane.
United Kingdom Patent Specification No. 1429982 of Mar. 31, 1976 discloses odorization of natural gas by introducing into it ethyl mercaptan or methyl mercaptan. This U.K. Patent Specification is abstracted at Volume 85, 1976, Number 96766h of Chem. Abstracts.
German Offenlegungsschrift 2347906 of Apr. 11, 1974 abstracted at Volume 81, 1974, Chem. Abstracts number 66119z discloses odorization of liquified natural gas with tetrahydro-2-methyl and/or 3-methyl thiophene dissolved in propane at -51.degree. to -29.degree. C.
Romanian Pat. No. 61082 of June 30, 1976 abstracted at Chem. Abstracts Volume 89, 1978, number 46081t, discloses the use of an odorant containing dimethyl sulfide, methyl mercaptan, ethyl mercaptan and diethyl sulfide with carbon monoxide, carbon dioxide, hydrogen and methane for odorizing natural gases.
Japan Kokai 79/58702 of May 11, 1979 abstracted at Volume 91, Chem. Abstracts, number 177874t discloses the odorization of liquified natural gas or city gas with stable t-heptyl mercaptan.
Japan Kokai 79/58701 of May 11, 1979 abstracted at Chem. Abstracts, Volume 91, number 195745f, discloses odorization of liquified natural gas or city gas with cyclohexane containing an organic sulfide or thiol such as ethyl mercaptan, isopropyl mercaptan, t-butyl mercaptan, dimethyl sulfide or methyl ethyl sulfide.
Japan Kokai 80/149392 of Nov. 20, 1980 abstracted at Volume 94, 1981, Chem. Abstracts number 124379r, discloses odorization of fuel gases such as natural gas, with a gaseous mixture of dimethyl sulfide, t-butyl mercaptan and isopropyl mercaptan.
Nothing in the prior art, however, discloses the unexpected, unobvious and advantageous effect of the mixture of 4-methyl-4-mercapto-2-pentanone and/or 2-methoxy-3-isobutyl pyrazine taken further together with other organic mercaptans or sulfides.
Although U.S. Pat. No. 3,630,750 discloses the use of 2-methoxy-3-isobutyl pyrazine in augmenting or enhancing the aroma of foodstuffs, particularly by imparting or augmenting an intense aroma of freshly chopped green bell peppers, and U.S. Pat. No. 3,773,524 discloses the use of keto mercaptans in augmenting or enhancing meat flavors, and 4-methyl-4-mercapto-2-pentanone, itself, is shown to cause an off flavor in cheese by Badings, J. Dairy Science, 50, Number 9, pages 1347 et seq. 1967, this prior art concerning augmenting or enhancing the organoleptic properties of consumable foodstuffs is not applicable to the art involving odorization of hydrocarbon gases used commercially.